Liquid phase sintering of silicon carbide with AlN/Y2O3, Al2O3/Y2O3 and SiO2/Y2O3 additions

Abstract

In this work, the influence of the additive system on the liquid phase sintering of silicon carbide has been investigated. The additives employed were mixtures of AlN/Y2O3, Al2O3/Y2O3 and SiO2/Y2O3. The total additive content was fixed at 20 vol.-%, maintaining the Y2O3 content in each additive system at 35 vol.-%. Cold isostatically pressed samples were sintered at 1900, 2000 and 2100 °C under Ar atmosphere during 30 min. The most promising results have been obtained by samples with AlN/Y2O3 additions sintered at 2000 °C, exhibiting the smallest weight loss of about 6% and the highest flexural strengths of about 433 MPa. Samples with Al2O3/Y2O3 and SiO2/Y2O3 additions exhibited high weight loss, because of reactions of Al2O3 and SiO2 with the SiC matrix, forming gaseous species such as Al2O, SiO and CO, resulting in depletion of the liquid phase, and, consequently, in inferior final densities and mechanical properties. Concerning the SiO2/Y2O3 additive system, the reactions seem to be completed already at temperatures below 1900 °C, turning this additive mixture unsuitable. The microstructural analysis indicated only the presence of the -SiC phase for all samples; no phase transformation of the -SiC into -SiC has been observed.